Hypertension treatment device and method for mitigating rapid changes in blood pressure

ABSTRACT

An implantable baroreflex activation device administers a special electrotherapy program that causes the device to apply electrotherapy to limit a rate of change of blood pressure increase associated with a blood pressure surge event such as a morning blood pressure surge (MBPS).

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates generally to medical devices and treatmentand, more particularly, to electrotherapeutic treatment of rapid changesin blood pressure.

Cardiovascular disease is a major contributor to patient illness andmortality. It also is a primary driver of health care expenditure,costing more than $326 billion each year in the United States.Hypertension, or high blood pressure, is a major cardiovascular disorderthat is estimated to effect over 50 million people in the United Satesalone. Of those with hypertension, it is reported that fewer than 30%have their blood pressure under control. Hypertension is a leading causeof heart failure and stroke. It is the primary cause of death in over42,000 patients per year and is listed as a primary or contributingcause of death in over 200,000 patients per year in the U.S.Accordingly, hypertension is a serious health problem demandingsignificant research and development for the treatment thereof.

Hypertension may occur when the body's smaller blood vessels(arterioles) constrict, causing an increase in blood pressure. Becausethe blood vessels constrict, the heart must work harder to maintainblood flow at the higher pressures. Although the body may tolerate shortperiods of increased blood pressure, sustained hypertension mayeventually result in damage to multiple body organs, including thekidneys, brain, eyes and other tissues, causing a variety of maladiesassociated therewith. The elevated blood pressure may also damage thelining of the blood vessels, accelerating the process of atherosclerosisand increasing the likelihood that a blood clot may develop. This couldlead to a heart attack and/or stroke. Sustained high blood pressure mayeventually result in an enlarged and damaged heart (hypertrophy), whichmay lead to heart failure.

Heart failure is the final common expression of a variety ofcardiovascular disorders, including ischemic heart disease. It ischaracterized by an inability of the heart to pump enough blood to meetthe body's needs and results in fatigue, reduced exercise capacity andpoor survival. It is estimated that approximately 5,000,000 people inthe United States suffer from heart failure, directly leading to 39,000deaths per year and contributing to another 225,000 deaths per year. Itis also estimated that greater than 400,000 new cases of heart failureare diagnosed each year. Heart failure accounts for over 900,000hospital admissions annually, and is the most common discharge diagnosisin patients over the age of 65 years. It has been reported that the costof treating heart failure in the United States exceeds $20 billionannually. Accordingly, heart failure is also a serious health problemdemanding significant research and development for the treatment and/ormanagement thereof.

Heart failure results in the activation of a number of body systems tocompensate for the heart's inability to pump sufficient blood. Many ofthese responses are mediated by an increase in the level of activationof the sympathetic nervous system, as well as by activation of multipleother neurohormonal responses. Generally speaking, this sympatheticnervous system activation signals the heart to increase heart rate andforce of contraction to increase the cardiac output; it signals thekidneys to expand the blood volume by retaining sodium and water; and itsignals the arterioles to constrict to elevate the blood pressure. Thecardiac, renal and vascular responses increase the workload of theheart, further accelerating myocardial damage and exacerbating the heartfailure state.

The body's systems responsible for control of blood pressure respond tothe overall activity level of the body. Typically, these systems cause adaily increase in blood pressure to accompany the change in activitylevels as the body transitions from a sleeping state to an active state.The incidence of acute cardiovascular events, such as myocardialinfarction (heart attacks), sudden cardiac death, and stroke, is knownto increase during the morning hours and is usually attributed to thesurge in early-morning blood pressure. Weekly variations, peaking onMondays, have also been reported, which may account for the higherfrequency of cardiovascular events on Mondays. See Murakami S, Otsuka K,Kubo Y, et al., Repeated ambulatory monitoring reveals a Monday morningsurge in blood pressure in a community-dwelling population, 17 Am JHypertens. 1179-83 (2004). Morning surges in blood pressure have alsobeen linked to strokes in the elderly. Kazuomi Kario, et al., MorningSurge in Blood Pressure as a Predictor of Silent and ClinicalCerebrovascular Disease in Elderly Hypertensives: A Prospective Study,107 Circulation 1401-06 (2003).

It has been known for decades that the wall of the carotid sinus, astructure at the bifurcation of the common carotid arteries, containsstretch receptors (baroreceptors) that are sensitive to the bloodpressure. These receptors send signals via the carotid sinus nerve tothe brain, which in turn regulates the cardiovascular system to maintainnormal blood pressure (the baroreflex), in part through activation ofthe sympathetic nervous system.

Electrical stimulation of the carotid sinus nerve (baropacing) haspreviously been proposed to reduce blood pressure and the workload ofthe heart in the treatment of high blood pressure and angina. Forexample, U.S. Pat. No. 6,073,048 to Kieval et al., which is incorporatedby reference herein in its entirety, discloses a baroreflex modulationsystem and method for stimulating the baroreflex arc based on variouscardiovascular and pulmonary parameters. Other implantable devices fortreating or monitoring high blood pressure or hypertension bystimulating various nerves and tissue in the body are known anddescribed, for example, in U.S. Pat. No. 3,650,277 (stimulation ofcarotid sinus nerve), U.S. Pat. No. 5,707,400 (stimulation of vagalnerve), U.S. Pat. No. 6,522,926 (stimulation of baroreceptors), and U.S.Pat. No. 6,529,771 (monitoring of patient cardiac status), all of whichare incorporated by reference herein in their entirety.

These, and other implantable electrotherapeutic hypertension treatmentscan control blood pressure by influencing the body's sense-responsesystem. Electrotherapy techniques can include fixed, continuousmonotherapy to effectuate an across-the-board reduction in bloodpressure, or dynamic therapy, in response to sensed blood pressure oractivity level, to effectuate condition- or demand-based blood pressurecontrol. U.S. Patent Application Publication No. 2005/0149130, which isincorporated by reference herein in its entirety, discusses adaptingelectrotherapy for hypertension treatment according to the patient'scircadian rhythm.

One drawback of existing hypertension electrotherapy systems is thesesystems are not especially adapted to address the problem of morningblood pressure surges, which, due to their apparent propensity fortriggering severe catastrophic cardiovascular events, merit specializedmanagement for minimizing their adverse effects.

BRIEF SUMMARY OF THE INVENTION

One aspect of the present invention is directed to a hypertensiontreatment device that administers electrostimulation to a patient'sbaroreceptors to selectively control blood pressure in the patient,wherein the administration of the electrostimulation is based, at leastin part, on the time of day. Preferably, the electrostimulation isadministered by the hypertension treatment device according to a profilethat is designed to reduce the severity of surges in morning bloodpressure surges (MBPS) of the patient by reducing thetime-rate-of-change of these morning surges.

According to one embodiment, a hypertension treatment device implantedin a patient includes a time base clock. One embodiment of the time baseclock is a real-time clock circuit that is configured to represent atleast the time of day. Preferably, the time base clock can alsorepresent the day of the week. The device is configured with a firsttransition time setting at which the patient is anticipated totransition from a state of relative inactivity to a state of relativelyhigher activity. In operation, the device executes a specialelectrotherapy program during a time window proximate in time to thefirst transition time setting. Preferably, the start of the time windowprecedes the first transition time setting, and the end of the timewindow succeeds the first transition time setting.

The special electrotherapy program causes the device to selectivelyapply electrostimulation such that the patient's blood pressure risesrelatively gradually in response to a low-to-high activity leveltransition occurring proximately in time to the first transition timesetting. The relatively gradual blood pressure rise is relative to therise that would occur in the absence the special electrotherapy program,and can be achieved by reducing the difference between the low-pressureand high-pressure levels, by extending the time duration during whichthe blood pressure rise occurs, or by a combination thereof.

According to one embodiment, as the time of day approaches thetransition time setting, (i.e., towards the end of the period ofrelative inactivity, but before the start of the transition to theperiod of higher activity of the patient), the special electrotherapyprogram either permits, or initiates, the patient's blood pressure torise, respectively, by either reducing the level of pressure-reducingelectrotherapy, or by applying pressure-increasing electrotherapy. In arelated embodiment, following the transition time setting, the specialelectrotherapy program administers pressure-reducing electrotherapy.Preferably, the level of pressure-reducing electrotherapy administeredsoon after the transition time setting by the special electrotherapyprogram is greater than a nominal level of electrotherapy appliedoutside of the time window of the special electrotherapy program.

In various embodiments, the hypertension treatment device incorporatesone or more sensors to facilitate heuristically determining thetransition time setting, recognizing the patient's actual transitionfrom low- to high-activity levels, and measuring the intensity of asurge in the patient's blood pressure as part of a control loop thatregulates the levels of electrotherapy to apply during the specialelectrotherapy program. The sensor(s) can work in conjunction with, orindependently from, the real-time clock-related functionality of thehypertension treatment device.

In a related embodiment, the hypertension treatment device includes acommunications circuit for interfacing with an external programmer. Inone embodiment, the programmer is integral with an appliance orinstrument used daily by the patient, such as an alarm clock, whereinits use pattern is predictive of the patient's actual transition time.The programmer can set or adjust the transition time setting.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a morning blood pressure surge (MBPS)in a patient, and includes curves representing the systolic bloodpressure as a function of time, and the rate of change of the systolicblood pressure, normalized to dP/dt per hour.

FIGS. 2A through 2C illustrate the effect of conventional electrotherapyof a continuous fixed level (monotherapy) on a patient's systolic bloodpressure curve during the MBPS.

FIGS. 3A-3C illustrate the effect of a special electrotherapy programthat administers a modulated electrotherapy dose that is designed toincrease the level of pressure-reducing therapy during the MBPSaccording to one aspect of the invention.

FIGS. 4A-4C illustrate a related technique for blunting the MBPSinstantaneous rates of change, in which the dosage of electrotherapy isreduced during a time interval preceding the onset of the MBPS accordingto one aspect of the invention.

FIGS. 5A-5C illustrate the effects on the patient's systolic bloodpressure curve of applying a special electrotherapy program thatincludes both the therapy dosage level decrease preceding the naturalstart of the morning surge as illustrated in FIGS. 4A-4C, and a therapylevel increase following the start of the morning surge as illustratedin FIGS. 3A-3C.

FIG. 6 is a diagram illustrating various components of an examplebaroreflex activation device according to one aspect of the inventionthat is implanted in a patient.

FIG. 7 illustrates one embodiment of a central processing unit (CPU) ofthe baroreflex activation device of FIG. 6.

FIG. 8 illustrates an example time window positioned around thetransition time of a MBPS, during which window a special electrotherapyprogram could be applied according to one aspect of the invention.

FIGS. 9A and 9B illustrate examples of special electrotherapy programprocess flows according to various embodiments of the invention.

FIG. 10 illustrates an example supervisory operating process for animplanted baroreflex activation device according to one embodiment thatdetermines when to apply the special electrotherapy program and when toapply a nominal electrotherapy dose based on the time.

FIGS. 11A-11D are block diagrams illustrating various exampleconfigurations of hypertension treatment systems according to variousembodiments having physiologic monitoring.

FIG. 12A is a flow diagram illustrating an example process according toone embodiment for recognizing the beginning and end of a blood pressuresurge using blood pressure sensing.

FIG. 12B is a flow diagram illustrating example process according to oneembodiment that can recognize and predict blood pressure surges based ona diversity system of sensors.

FIG. 13 illustrates an example control system according to oneembodiment for regulating the blood pressure, including regulating therate of change of blood pressure, to prevent rapid changes such as thoseoccurring during MBPS events.

While the invention is amenable to various modifications and alternativeforms, specifics thereof have been shown by way of example in thedrawings and will be described in detail. It should be understood,however, that the intention is not to limit the invention to theparticular embodiments described. On the contrary, the intention is tocover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a curve illustrating a typical systolic blood pressureprofile for a hypertension patient during the morning hours. Curve 100is plotted against vertical access 102 and represents the patient'ssystolic blood pressure in mmHg. Curve 104 represents the rate of changeof curve 100 and is plotted against vertical access 106, which isnormalized to mmHg per hour. As can be seen from curves 100 and 104, atransition point 108 exists just before 7:00. Transition point 108coincides with the time when the patient awakens from a sleep state andtransitions from a state of relatively low activity to a period ofrelatively higher activity level.

Beginning at transition point 108, curve 100 depicts the patient's bloodpressure rising sharply from about 160 mmHg to nearly 120 mmHg. Thisphenomenon is known as the morning blood pressure surge (MBPS) and, asdescribed above, has been associated with the incidents of heartattacks, strokes, and other catastrophic cardiovascular events. Thepatient's blood pressure increases at a rapid rate until about 9:15, andthen stabilizes at its final level. The rate of blood pressure increasepeaks between 7:30 and 8:00 at about 40 mmHg per hour, as indicated at110.

One aspect of the present invention is directed to an electrotherapymethod and apparatus for reducing severity of the MBPS. Reducing theseverity of the MBPS can include slowing the rate of blood pressureincrease associated with the surge, reducing the difference between thepre-surge and post-surge blood pressure levels, or administering atreatment that is a combination thereof.

FIGS. 2A through 2C illustrate the effect of conventional electrotherapyof a continuous fixed level (monotherapy) on a patient's systolic bloodpressure curve during the MBPS. As shown in FIG. 2A, curve 100′ is thesame as 100 of FIG. 1 and represents the patient's blood pressurepattern in the absence of any electrotherapy. Curve 200 of FIG. 2Arepresents the patient's blood pressure pattern over the same timeperiod and while the patient receives a constant level ofpressure-reducing electrotherapy. The therapy level is illustrated as afunction of time at curve 220 in FIG. 2C. As can be seen in FIG. 2A, themonotherapy provides a constant reduction in blood pressure throughoutthe time period shown. While the blood pressure pattern depicted bycurve 200 is overall lower than blood pressure pattern 100′, the MBPSbetween the two curves has an identical rate of change profile. FIG. 2Bshows curves 104′ and 204, which respectively depict the rates of changeof curves 100′ and 200. Curves 104′ and 204 are overlaid on one another,and it can be seen that both are identical to curve 104 of FIG. 1.Therefore, the continuous monotherapy does nothing to temper themagnitude of the transient change in blood pressure caused by the MBPS.

FIGS. 3A-3C illustrate the effect of a special electrotherapy programthat administers a modulated electrotherapy dose that is designed toincrease the level of pressure-reducing therapy during the MBPS. FIG. 3Ashows three blood pressure curves: curve 100′; curve 200′, which isidentical to curve 200 of FIG. 2A and repeated in FIG. 3A for reference;and curve 300, which is the blood pressure pattern achieved byadministering modulated electrotherapy having a profile depicted bytherapy curve 320 of FIG. 3C. For reference, FIG. 3C also shows therapylevel curve 220′, which is identical to therapy level curve 220 of FIG.2C. Referring again to FIG. 3A, blood pressure curve 300 has the samepre-surge and post-surge levels as curve 200′, but has a more steadyrate of change during the MBPS that peaks at slightly greater thanone-half of the rate of change of curve 200′. This result is depicted inFIG. 3B. Curve 304 represents the rate of change of curve 300. Forreference, curves 104′ and 204′ are also shown. Curve 204′ is identicalto curve 204 of FIG. 2B.

FIGS. 4A-4C illustrate a related technique for blunting the MBPSinstantaneous rates of change. Instead of increasing the dosage of thepressure-reducing electrotherapy during the surge as with the techniqueof FIGS. 3A through 3C, the technique of FIGS. 4A through 4C involvesreducing the dosage of the pressure-reducing electrotherapy during atime period prior to the start of the surge. Referring first to FIG. 4C,special electrotherapy program curve 420 is shown superimposed overelectrotherapy curve 220′. Electrotherapy curve 420 follows a profile inwhich, starting at around 5:15, the therapy dose is progressively cutback, and then progressively increased back to its nominal level suchthat the therapy is returned to its nominal level shortly after thestart of the MBPS. The effect of the therapy profile having curve 420 isillustrated by blood pressure curve 400 of FIG. 4A. Curve 400 has a morelinear profile for the blood pressure increase than reference curves100′ and 200′. Also, the starting point of the pressure increase occursearlier than for curves 100′ and 200′. In FIG. 4B, curve 404 representsthe rate of change of curve 400. Curve 404 peaks at a level that isapproximately one-half that of reference curves 104′ and 204′.

FIGS. 5A-5C illustrate the effects on the patient's systolic bloodpressure curve of applying a special electrotherapy program thatincludes both the therapy dosage level decrease preceding the naturalstart of the morning surge as described with reference to FIGS. 4A-4C,and a therapy level increase following the start of the morning surge asdescribed above with reference to FIGS. 3A-3C. This therapy profile isillustrated in FIG. 5C. Therapy program curve 520 shows a period ofreduced therapy level followed immediately by a period of increasedtherapy level. Curve 500 of FIG. 5A illustrates the result on thepatient's blood pressure over time. Resulting blood pressure curve 500has a substantially linear pressure increase that begins before thenaturally-occurring start of the MBPS and ends by merging into curve200′ to arrive at the blood pressure level at the conclusion of theMBPS. FIG. 5B shows curve 504, which illustrates the rate of change ofcurve 500. Curve 504 has a peak level that is around one-third the peaklevel of reference curves 104′ and 204′.

FIG. 6 is a diagram illustrating an example baroreflex activation device600 that is implanted in a patient 602. Implanted device 600 includes acentral processor unit (CPU) 604, which may include one or moremicroprocessors or microcontrollers, for example, that is configured tocontrol the operation of the device. CPU 604 is configured to cause thedevice to administer the electrotherapy via electrotherapy circuit 606and electrodes 608. A communications circuit 610 is interfaced with CPU604 and is used for communicating information between CPU 604 andequipment external to the patient 602, such as a device programmer (notshown). Baroreflex activation device 600 also includes a power sourcesuch as a battery 612, and power conditioning circuitry 614 forconverting the battery power into various power supplies suitable forpowering each sub-system of the device. Optionally, CPU 604 can detectat least one physiologic condition of patient 602 via patient monitoringcircuitry 616 and at least one sensor 618.

FIG. 7 illustrates one embodiment of CPU 604. CPU 604 includes amicroprocessor core 700; read-only memory (ROM) 702 for storinginstructions; random access memory (RAM) 704 for use as data gathering,or scratchpad memory during operation; input/output (I/O) bus drivingcircuitry 706 for transmitting and receiving information via, andcontrolling the use of, I/O bus 707; analog-to-digital (A/D) converter708 for converting analog signals received via analog inputs 709 into adigital format for use by microprocessor core 700; and clock 710 forproviding a time base for use by microprocessor core 700. An internalCPU interconnect 712 provides an interface between the various CPUcomponents, and can include conventional data exchange hardware, such asa data bus, an address bus, and control lines (not shown).

In one embodiment, the clock 710 is a real-time clock (RTC) that keepstrack of day, date, and time, including year, month, hour, minutes, andseconds, and feeds this time information to microprocessor core 700 whenprompted. In one embodiment, clock 710 simply provides a reliable timerthat enables CPU 604 to generally monitor the passage of time.Microprocessor core 700 can utilize the simple time base informationprovided via clock 710 to calculate the time of day, date, day of theweek, or time duration since a particular event. In turn, thiscalculated time information can be used by the microprocessor core 700to determine the starting time of the expected blood pressure rise ofthe patient incident to an expected increase in the patient's activitylevel. Preferably, clock 710 and/or CPU 604 keeps track of the day ofthe week in addition to the time of day. For example, in treating apatient who is on a Monday-Friday work schedule, the blood pressuresurges on Monday-Friday mornings may be treated differently (such asmore aggressively) than morning surges on weekends. Similarly, keepingtrack of the days of the week would enable treating Monday morningsurges more aggressively than Tuesday-Friday surges, for example.Alternatively, CPU 604 may also keep track of days of month/year toadjust for holidays, daylight savings time, seasonal changes, and thelike.

A baroreflex activation device according to one embodiment of theinvention does not require a hemodynamic monitoring sub-system to detectan indication for applying increased or decreased dosage levels ofelectrotherapy. According to one embodiment, a hypertension treatmentdevice implanted in a patient includes a time base clock. One embodimentof the time base clock is a real-time clock circuit that is configuredto represent at least the time of day. Preferably, the time base clockcan also represent the day of the week. The device is configured with afirst transition time setting at which the patient is anticipated totransition from a state of relative inactivity to a state of relativelyhigher activity. In operation, the device executes a specialelectrotherapy program during a time window proximate in time to thefirst transition time setting. Preferably, the start of the time windowprecedes the first transition time setting, and the end of the timewindow succeeds the first transition time setting. In this regard, oneembodiment responds proactively to an expectation, prediction, or,generally, to an anticipation of a future MBPS by initiating the specialelectrotherapy program before the actual start of the MBPS.

The special electrotherapy program causes the device to selectivelyapply electrostimulation such that the patient's blood pressure risesrelatively gradually in response to a low-to-high activity leveltransition occurring proximately in time to the first transition timesetting. The relatively gradual blood pressure rise is relative to therise that would occur in the absence the special electrotherapy program,and can be achieved by reducing the difference between the low-pressureand high-pressure levels, by extending the time duration during whichthe blood pressure rise occurs, or by a combination thereof.

FIG. 8 illustrates an example window positioned in time around thetransition time of a MBPS, during which window a special electrotherapyprogram would be applied. FIG. 8 shows reference blood pressure curve100′, which represents a patient's MBPS beginning at just before 7:00,as indicated at time 802. As described above with reference to FIGS.3A-5C, various MBPS management schemes according to embodiments of theinvention include special electrotherapy programs that can beadministered during the transition window that includes: (a) a pre-surgetime interval 804 that precedes the start of the surge (at time 802) bya predetermined duration; (b) a post-surge time interval 806 that beginsat the surge start time 802 and lasts for a predetermined duration; or(c) during a combined pre- and post-surge time interval 808 thatincludes both intervals 804 and 806.

During pre- and post-surge intervals 804 and 806, respectively, thespecial electrotherapy program preferably applies different dosages ofelectrotherapy to reduce the peaks of the instantaneous changes in bloodpressure. FIG. 9A illustrates an example special electrotherapy programprocess 900. Process 900 begins at the start of interval 804. Asupervisory process that initiates special electrotherapy programprocess 900 is described below with reference to FIG. 10. Specialelectrotherapy program process 900 is time-based in the sense that eachelectrotherapy administration step of the process is maintained for apredetermined length of time. Also, persons skilled in the relevant artswill appreciate that the electrotherapy dosages and durations of theprocess steps, as well as the number of process steps can be variedwithin the spirit of the invention.

Process 900 begins when a nominal electrotherapy program is beingapplied. The nominal electrotherapy program is typically a fixed dosageselected to provide a generally steady reduction of the patient's bloodpressure; however, the nominal electrotherapy program can be a variabledosage that is adjustable or dynamically controllable based on thecircumstances. In one embodiment, the nominal electrotherapy programapplied by the implanted baroreflex activation device provides at leasttwo nominal electrotherapy dosages, such as one nominal dosage forperiods of relative inactivity of the patient (such as sleep), and onefor periods of relatively higher activity levels. There can be othernominal dosages for various periods of intermediate activity levels.Essentially, however, in the present context, the nominal electrotherapyprogram refers to the output of the implanted baroreflex activationdevice in the absence of any blood pressure surges.

At step 902 of process 900, the electrotherapy is reduced from thenominal (e.g., sleep time) dosage by a factor of 80%, for example, andmaintained for 90 minutes. At step 904, the electrotherapy is sharplyincreased to 140%, for example, of the nominal (e.g., awake time)dosage. Step 904 is preferably timed to coincide with the patient'sactivity level transition time (i.e. shortly before the patient wakesup). At step 906, the electrotherapy dosage is returned to its nominal(e.g. awake time) level(s) following the expected duration of the MBPS.Process 900 is designed to reduce the magnitude and slope of the MBPS byfirst causing the patient's blood pressure to increase during thepre-surge interval, and then by reducing the magnitude of the finallevel of the MBPS. Additionally, process 900 is design to blunt the MBPSby administering aggressive electrotherapy during the surge.

FIG. 9B illustrates special electrotherapy process 950, which is avariation of process 900. In process 950, control of the patients bloodpressure is achieved with finer granularity. At step 952, the nominalelectrotherapy dosage is reduced by 33% and maintained for 30 minutes.At step 954, the dosage is further reduced by 50% and maintained for 30minutes. At 956, the electrotherapy is discontinued entirely, and thisstate is maintained for 30 minutes. At step 958, the electrotherapy isre-administered at the low level of 20% of the nominal dosage. Duringthese steps, the electrotherapy has been cut back to permit thepatient's blood pressure to rise gradually in a controlled manner. As avariant of this embodiment, pressure-increasing electrotherapy can beapplied to force the patient's blood pressure to increase in acontrolled manner.

At step 960, the electrotherapy is increased sharply to 115% of thenominal level, and maintained for 30 minutes. Step 960 is timed suchthat the start of the MBPS occurs during the 30-minute period. At steps962 and 964, the electrotherapy is further increased sequentially to140% and 150% of nominal to aggressively counter-act the pressure riseof the MBPS. At step 966, timed to be executed towards the end of theMBPS, the aggressive electrotherapy dose is cut back to about 120% ofnominal. At step 968, the aggressive electrotherapy dosage is furthercut back to the nominal level to permit the patient's blood pressure tostabilize at the final, post-MBPS, level. In one embodiment, thestepwise sequence of process 950 has therapy dosage levels and timedurations such that the controlled MBPS is gradual and has a generallyconstant slope.

FIG. 10 illustrates an example supervisory operating process 1000 for animplanted baroreflex activation device that determines when to apply thespecial electrotherapy program and when to apply a nominalelectrotherapy dose based on the time. At 1002, the CPU of the devicereads the clock to determine the current time. In this context, thecurrent time can be the time of day, or a duration of time lapse since aparticular reference time or event. At 1004, the CPU determines whetherthe current time is within the pre-defined window associated with thetransition window. If the blood pressure is outside of the window, thenominal electrotherapy dose or program is applied, as indicated at 1006.If, on the other hand, the current time is within the pre-definedtransition window, the special electrotherapy program is applied, asindicated at 1008.

Referring again to FIG. 8, the transition window 804, 806, or 808 can beset by a variety of techniques. According to one embodiment, thetransition window is set in the implanted baroreflex activation deviceby an external device programmer that has a transceiver capable ofcommunicating with a matching transceiver of the implanted device.Preferably, the external programmer has a simple time-setting functionthat can be operated by the patient. For example, the externalprogrammer can be part of an alarm clock, GPS receiver, personal digitalassistant (PDA), cellular telephone, or other common appliance. Thewakeup time setting in the appliance is communicated to the implanteddevice and treated as the anticipated wake-up time. The beginning andend times of the transition window are then established around theanticipated wake-up time.

In a related embodiment, the implanted baroreflex device includes afeature that enables at least a portion of the special electrotherapyprogram to be disabled. For example, if the patient expects to sleep in,travel, or otherwise deviate from the patient's usual routine, thepatient can use an external programmer or other device for communicatinga signal to the implanted baroreflex activation device (such as amagnet). In response to the disable command, the special electrotherapyprogram can be adjusted to cancel the function that anticipates theoccurrence of the MBPS, for example.

In a related embodiment, the external programmer programs the wakeuptime set point into the implanted baroreflex activation device soonafter the set-point is entered into the programmer by the patient. Theimplanted device uses its time base clock to recognize the start of thetransition window as the current time approaches the wake-up time. In afirst variation of this embodiment, the external programmer keeps trackof the wake-up time set point and the current time, and signals to theimplanted device when the time of the start of the transition window hasbeen reached. In this first variation embodiment, the implanted devicedoes not require a time base clock because the timing of the transitionwindow is taken care of by the external programmer (which is presumed tobe within communications range of the implanted device at least duringthe execution of the special electrotherapy program). In a secondvariation embodiment, both, the external programmer, and the implanteddevice keep track of the current time and compare the current timeagainst the wake-up set point. Prior to initiating the specialelectrotherapy program, the implanted device and external programmercommunicate with one another to confirm that the special electrotherapyprogram is to be executed at the correct time in view of the wake-uptime set point and current time reading.

If necessary, the time base clock in the implanted device can beadjusted by using the external programmer, which may be optionallyconnected to a networked time source such as the Internet, GPS, or radiostations. If the patient should change locations, the time base clockcould be updated according to the local time settings.

According to one aspect of the invention, a hypertension treatmentsystem including an implantable baroreflex activation sub-system furtherincludes a physiologic monitoring sub-system that can communicate withthe implantable baroreflex activation sub-system. The physiologicmonitoring sub-system generally includes at least one sensor, andmonitoring circuitry that is interfaced with the sensor. The at leastone sensor detects and/or measures a physiologic condition of thepatient; the monitoring circuitry powers the sensor (if needed), readsthe sensor, and output a signal representing the sensor reading.

In various embodiments, different sensors and different combinations ofsensors are used. Persons skilled in the relevant arts will appreciatethat this aspect of the invention is not limited to any particularsensing technology or arrangement. Examples of sensing include:hemodynamic sensing, motion sensing, temperature sensing, positionalsensing, photo sensing, neural activity sensing, and the like.Hemodynamic sensing includes, but is not limited to, heart rate sensing,ECG activity sensing, blood pressure sensing, pulse oxymetry sensing,respiration activity sensing (such as minute respiration), and the like.

The monitoring circuitry includes circuits for receiving sensor output,as well as any signal conditioning or processing circuits for generatingan output signal. Certain sensors may require power to be supplied, inwhich case the corresponding monitoring circuitry will include theappropriate supply power to energize the sensors. In embodiments havingmultiple different types of sensors, the monitoring circuitry includes,collectively, each corresponding circuitry for each different sensor. Inone embodiment, the monitoring circuitry includes analog-to-digital(A/D) conversion, data storage, and data analysis functionality, whichcan provide information in a summary format as its output. Examples ofsummary outputs include data aggregation and statistically-analyzeddata.

The interface between each sensor and each corresponding monitoringcircuitry can take any suitable form within the spirit of this aspect ofthe invention, without necessarily a 1-1 correspondence. For example,some sensors can be integrally assembled with their respectivemonitoring circuits; whereas other sensors can be more remote from theircorresponding monitoring circuit (e.g., interconnected via cable orwireless communication channel). The output signal from the monitoringcircuitry can be in any suitable form for communication with the otherhypertension treatment system sub-systems, including, but not limitedto, an analog DC voltage or current signal, an analog modulated signal,a discretized analog signal, and/or a digital signal. The output signalcan be communicated via any suitable channel or medium, including byelectrical conduction, by electromagnetic transmission, by ultrasonictransmission, and the like.

FIGS. 11A-11D are a block diagrams illustrating various exampleconfigurations of hypertension treatment systems having physiologicmonitoring. Referring to FIG. 11A, hypertension treatment system 1100 aincludes baroreflex activation device 1104 a implanted in patient 1102a. Monitoring circuit 1106 a is integrally a part of implantedbaroreflex activation device 1104 a. Sensor 1108 a, also implanted inpatient 1102 a, is positioned outside the housing of baroreflexactivation device 1104 a and electrically interfaced with monitoringcircuitry 1106 a.

In FIG. 11B, example hypertension treatment system 1100 b has anexternal (i.e. non-implanted) sensor 1110 b at the outside surface ofthe patient 1102 b. Baroreflex activation device 1104 b is implanted inpatient 1102 b, and receives sensor information via external monitoringcircuitry 1112 b. In this embodiment, implanted baroreflex activationdevice 1104 b utilizes a communications circuit (not shown) to receivethe output signal from monitoring circuitry 1112 b. After receiving theoutput signal, baroreflex activation device 1104 b appliesdecision-making criteria or control logic functionality to interpret oranalyze the sensor reading.

The example arrangement depicted in FIG. 11C includes baroreflexactivation device 1104 c implanted in patient 1102 c. External sensor1110 c reads a physiologic condition of patient 1102 c, and feeds thereading to external monitoring circuit 1112 c. Sensor data collected viamonitoring circuit 1112 c is provided to external programmer 1114 c foranalysis. External programmer 1114 c computes operating parameters forimplanted baroreflex activation device 1104 c, and programs baroreflexactivation device 1104 c to provide a suitable electrotherapy dosagebased on the sensor data. This embodiment differs from the embodimentdescribed above with reference to FIG. 11B in that the presentembodiment utilizes an external programmer for analyzing the sensordata, whereas in the embodiment of FIG. 11B, the baroreflex activationdevice self-programs based on the sensor data.

In FIG. 11D, example hypertension treatment system 1100 d includesbaroreflex activation device 1104 d implanted in patient 1102 d.Baroreflex activation device 1104 d has integral monitoring circuitry1106 d interfaced with implanted sensor 1108 d. Also, hypertensiontreatment system 1100 d includes external sensor 1110 d interfaced withexternal monitoring circuitry 1114 d. Internal sensor 1108 d andexternal sensor 1110 d can be the same, or different types of sensors.Baroreflex activation device 1104 d receives sensor information fromboth monitoring circuits 1106 d and 1114 d, analyzes the sensor dataprovided by each, and adjusts its operating point based on theinformation from the two sensors.

According to one embodiment, the sensor information is used to recognizethe MBPS and adjust the baroreflex activation electrotherapy tobeneficially control the pressure rise. In a related embodiment, thesensor information is used to characterize patterns of changing activitylevels of the patient, enabling the prediction of a future MBPS startingtime. In another related embodiment, hemodynamic sensing facilitatescharacterizing the patient's MBPS curve, which enables predeterminingthe electrotherapy dosages in the special electrotherapy program appliedduring and/or before the surge. Preferably, the sensor(s) are designedto work in conjunction with the time-base clock of the hypertensiontreatment device.

FIG. 12A is a flow diagram illustrating an example process 1200 forrecognizing the beginning and end of a blood pressure surge using bloodpressure sensing. The data gathered by process 1200 can also be used forcharacterizing the shape of the time-curve of the blood pressure surge.As illustrated, process 1200 begins at a time when there is no bloodpressure surge. At step 1202, blood pressure measurements are takenbefore any surge is recognized. The blood pressure measurements can betaken at predetermined time intervals or otherwise, so long as the timebetween successive measurements is measured or tracked. At step 1204,the rate of pressure change dP/dt is computed for at least twosuccessive blood pressure measurements. At step 1206, the rate dP/dt iscompared against a rate limit for what is deemed to be a normal rate ofpressure change. The limit dP/dt is based on the time-rate-of-change ofthe blood pressure, and can also be based on a magnitude threshold or ona duration threshold such that, for example, dP/dt computations for avery small pressure differential or lasting a very short duration aredisregarded.

If the computed dP/dt does not exceed the “normal” limit, then themeasurements and computations of steps 1202 and 1204 are repeated. If,however, the computed dP/dt exceeds what is considered a normal rate ofvariation, the event is considered to be the start of a blood pressuresurge, and, at step 1208, the process indicates that a surge has beenidentified. At step 1210, the time and day, as well as the startingblood pressure value of the surge are recorded. Blood pressuremeasurements are taken as the surge continues, as indicated at step1214, and, at step 1216, the rates of pressure changes for thesemeasurements are computed. At 1218, the rate of pressure change iscompared against the limit for what is considered normal variation. Ifthe measured dP/dt falls back into the normal range, the completion ofthe surge is indicated at 1220, and the day, time, and final bloodpressure is recorded at step 1222.

In one embodiment, the blood pressure measurements made prior to,during, and following, each surge event, are analyzed for multiplesurges. From this analysis, characteristics that are common to all (ormost) of the surge events are identified. These common characteristicscan include the duration, intensity, dP/dt over time, and other relevantfeatures of the surge events in the patient. In a related embodiment,the common characteristics are used to predict the time of the surgeonset. From such information, in a related embodiment, the specialelectrotherapy program can be manually or automatically adjusted toprovide electrotherapy dosage levels, as functions of time, that areespecially suited to treat the surges experienced by the patient. Theseare examples of heuristic learning modes of operation of a hypertensiontreatment system according to one aspect of the invention.

FIG. 12B is a flow diagram illustrating example process 1230 that canrecognize blood pressure surges based on a diversity system of sensors.Process 1230 also includes a function that can predict futureoccurrences of blood pressure surges. The predictive function is basedon using historic records of past surge events, and correlatingpresent-time measurements with historic data trends to develop aprobabilistic system of anticipating future blood pressure surge events.At step 1232, the time base measurement is read and stored. The timebase measurement can be the time of day, day of week, and the like, inseconds, relative to the calendar or 24-hour clock. The time basemeasurement can also be an independent time measurement not necessarilysynchronized with, or otherwise related to, any external time base.

At steps 1234, 1236, and 1238, physiologic measurements are made. Atstep 1234, the heart rate is measured and stored. At 1236, the patient'smotion and/or position (e.g., lying down, or upright) is read andstored. At 1238, the patient's respiration rate is read and stored. Eachof these physiological measurements is indicative of the patient'sactivity level. From these measurements, the patient's wake/sleep statecan be inferred. When combined with the time base measurement, theduration of any particular activity state can be monitored, and thetransition from one type of activity level to another can be detected.Because blood pressure surges are known to accompany sleep-to-waketransitions, the onset of a blood pressure surge can be inferred withoutthe need for a direct blood pressure measurement. For illustrativepurposes, these physiologic measurements do not include a direct bloodpressure measurement. However, in a related embodiment, a blood pressuremeasurement can be included among these physiologic measurements foradditional patient monitoring accuracy.

Each type of physiologic measurement, and each combination ofmeasurements (including the time-based measurements) may have adifferent strength of correlation to the patient's actual activitystate. Therefore, at step 1240, different weighting is applied to thevarious measurements, and the weighted measurements are aggregated toproduce a basis for inferring the existence of a blood pressure surgeevent. At step 1242, a logical test is applied to determine whether ornot a surge is properly inferred from the physiologic measurements. If asurge is recognized at step 1242, the system provides an indication tothat effect, and the physiologic measuring is continued.

If a surge is not recognized according to the logical test applied, thecurrent physiologic measurements are analyzed in light of historicmeasurements for predicting the onset of a surge event. For example, ifthe patient is believed to be in a sleep state, the historic duration ofthe sleep state may suggest an increased likelihood for the surge tooccur at about the six-hour mark since the start of the sleep state.Based on a pattern of sleep states, the historic data may indicate thatafter every seventh extended sleep period, the blood pressure surge isof a higher intensity, suggesting an earlier application of the specialelectrotherapy program with more aggressive treatment.

The result of the predictive analysis is a probability score. Forexample, at step 1248, a probability score is computed for thelikelihood of surge occurrence in the next two-hour period. If thelikelihood is relatively high, such as greater than 80%, as depicted atstep 1250, the process returns an indication of a surge prediction atstep 1252. If the probability is not sufficiently high to report, thephysiologic measurements are re-iterated. The surge prediction can beresponded to by initiating the special electrotherapy program to beginpermitting the patient's blood pressure to increase prior to the onsetof the surge. The surge detection output can be responded to by changingthe special electrotherapy program from pre-surge electrotherapy dosagesto more aggressive treatment during the surge event.

Methods of predicting, detecting, and characterizing blood pressuresurges can be used independently from, or in conjunction with,closed-loop control of the blood pressure surges. Closed-loop surgecontrol utilizes physiologic sensing to continuously feed backinformation representing the effect of the baroreflex activationelectrotherapy to the baroreflex activation device. In this manner, thebaroreflex activation device can apply electrotherapy dosage accordingto a dynamically-adjustable set point to continuously maintain a desiredblood pressure commensurate with the patient's activity level.

FIG. 13 illustrates an example control system 1300 for regulating theblood pressure, including regulating the rate of change of bloodpressure to prevent rapid changes such as those occurring during MBPSevents. A blood pressure (BP) set point 1302 is provided to the system.Set point 1302 is a target blood pressure that the system will achieveby adjusting the level of electrotherapy dosage. To achieve a desiredrate of change of blood pressure, BP set point 1302 is provided as afunction of time representing rate of change that is preferably lessthan the maximum permissible dP/dt. Thus, set point 1302 can be stable,or time-variable, depending on the circumstances surrounding the surgeevent.

Control system compares set point 1302 with an actual blood pressuremeasurement 1304 to produce an error signal 1306. The error signal 1306is operated on by proportional-integral-differential controls 1308,1310, and 1312, respectively. Proportional control 1308 includes aproportional weighting constant K_(P); integral control 1310 includes anintegral weighting constant K₁; and differential control 1312 includesdifferential weighting constant K_(D). The output of each control typeis aggregated to produce a control signal 1314. The baroreflexactivation device applies an electrotherapy dosage 1316 according to thecontrol signal 1314, which results in a controlled blood pressure 1318in the patient.

Utilizing a real-time control system such as system 1300 providesdynamic blood pressure and rate of pressure change control that isindependent of any deviations in the patient's routine, schedule, orphysiology. A preferred embodiment will utilize a combination of:diversity sensing of physiologic indicators to assess activity level;real-time blood pressure measurement; blood pressure surge predictionbased on physiology, time, and historic pattern data; and real-timecontrol to regulate pressure according to the special electrotherapyprogram to blunt the MBPS.

Various modifications to the invention may be apparent to one of skillin the art upon reading this disclosure. Therefore, the above is notcontemplated to limit the scope of the present invention.

1. A method of operating an implantable baroreflex activation device,the method comprising: administering a nominal electrotherapy program bythe device; and in response to a morning blood pressure surge (MBPS),initiating a special electrotherapy program that causes the device toapply electrotherapy to limit a rate of change of blood pressure rise.2. The method of claim 1, wherein the initiating of the specialelectrotherapy program occurs based on a passage of time.
 3. The methodof claim 1, wherein the special electrotherapy program includes aselectable dosage level, and further comprising: selecting theselectable dosage level based on a day of the week.
 4. The method ofclaim 1, wherein the initiating of the special electrotherapy programoccurs based on a programmable parameter of the implantable baroreflexactivation device.
 5. The method of claim 1, wherein the initiating ofthe special electrotherapy program occurs proactively in response to ananticipation of the MBPS.
 6. The method of claim 5, wherein the specialelectrotherapy program includes: a first portion that reduces theelectrotherapy prior to the start of the blood pressure surge event suchthat blood pressure rises; and a second portion that increases theelectrotherapy after the start of the blood pressure surge event.
 7. Themethod of claim 6, wherein the second portion increases theelectrotherapy to a dosage level that exceeds a nominal dosage levelapplied in the absence of the special electrotherapy program.
 8. Themethod of claim 1, further comprising: sensing a physiologic conditionwith a sensor.
 9. The method of claim 8, further comprising: controllingthe special electrotherapy program based on the sensing of thephysiologic condition.
 10. The method of claim 8, wherein the specialelectrotherapy program is initiated based on the sensing of thephysiologic condition.
 11. An implantable baroreflex activation system,comprising: a set of electrodes configured for electrical coupling withbaroreceptors; an electrotherapy circuit electrically coupled with theset of electrodes; a processor electrically coupled with theelectrotherapy circuit, and including operating logic that controlsadministration of electrotherapy by the electrotherapy circuit; whereinthe processor includes program logic that causes the electrotherapycircuit to: administer a nominal electrotherapy program during anabsence of any blood pressure surge event; and administer a specialelectrotherapy program to control blood pressure rise associated with ablood pressure surge event.
 12. The implantable baroreflex activationsystem of claim 11, wherein the special electrotherapy program includes:a first portion that reduces the electrotherapy prior to the start ofthe blood pressure surge event such that blood pressure rises; and asecond portion that increases the electrotherapy after the start of theblood pressure surge event.
 13. The implantable baroreflex activationsystem of claim 11, wherein the processor includes a time base; andwherein the special electrotherapy program is initiated at apredetermined time base value.
 14. The implantable baroreflex activationsystem of claim 11, further comprising: a physiologic sensor interfacedwith the processor; wherein the special electrotherapy program isinitiated based on a physiologic condition measured by the physiologicsensor.
 15. The implantable baroreflex activation system of claim 11,further comprising: a physiologic sensor interfaced with the processor;wherein the special electrotherapy program is controlled based onmeasurements made by the physiologic sensor.
 16. The implantablebaroreflex activation system of claim 11, further comprising: aphysiologic sensor interfaced with the processor; wherein the specialelectrotherapy program is scheduled based on measurements made by thephysiologic sensor.
 17. The implantable baroreflex activation system ofclaim 11, further comprising: a physiologic sensor interfaced with theprocessor; wherein the program logic includes analysis of storedhistorical measurements made by the physiologic sensor, wherein theanalysis is utilized to predict a future blood pressure surge event. 18.An implantable baroreflex activation system, comprising: electrode meansfor electrical coupling with baroreceptors; electrotherapyadministration means electrically coupled with the set of electrodes,the electrotherapy administration means including: nominalelectrotherapy program means for controlling blood pressure during anabsence of any blood pressure surge event; and special electrotherapyprogram means for controlling blood pressure rise associated with ablood pressure surge event.